U.S. Pat. No. 8,304,729 to Snider proposes methods, systems and apparatuses that detect, classify and locate flash events. In some implementations, some of the methods detect a flash event, trigger an imaging system in response to detecting the flash event to capture an image of an area that includes the flash event, and determines a location of the flash event.
U.S. Pat. No. 8,421,015 to Scott et al., discloses an event detection and classification system which uses a type of optical sensing component, a Position Sensing Detector Focal Plane Array (PSD-FPA). The PSD-FPA provides for high-speed operation that allows for accurate sensing of fast artifacts that are unique to weapons fire and enables precise location of optical phenomenon. The system detects and classifies events, particularly weapons fire, and rejects false alarms. An optical lens sub-system focuses light onto a PSD-FPA, which senses the photons and generates electrical signals associated with individual elements of the PSD-FPA. These signals are processed to identify and classify weapons-related or other events. Background subtraction, variable gain, time-intensity and time-location correlation, digital filtering, Fourier analysis, and wavelet analysis are all used to successfully classify the events while rejecting false alarms.
U.S. Pat. No. 7,619,754 to Riel et al. discloses curved sensor array configurations and methods of processing the data gathered by the sensors. A 2 dimensional embodiment comprises singular ring of sensors that can monitor sources in a 2 dimensional plane. A sensor directly facing a target produces a maximum response. As the angle of a sensor relative to the target increases, the response decreases. Fitting the sensor response amplitudes to a 2D Gaussian curve and calculating the peak of the curve allows a very accurate calculation of the angular direction of the target. A 3D embodiment comprises sensors distributed over the surface of a sphere in order to monitor multiple targets in any spatial orientation. Again, the sensor amplitude data is fitted to a 3D curve or surface such as a Gaussian surface. The present invention can resolve more than one target using deconvoluting techniques.
U.S. Pat. No. 3,936,822 to Hirschberg discloses a round detecting method and apparatus for automatically detecting the firing of weapons, such as small arms, or the like. Radiant and acoustic energy produced upon occurrence of the firing of the weapon and emanating from the muzzle thereof are detected at known, substantially fixed, distances therefrom. Directionally sensitive radiant and acoustic energy transducer means directed toward the muzzle to receive the radiation and acoustic pressure waves therefrom may be located adjacent each other for convenience. In any case, the distances from the transducers to the muzzle, and the different propagation velocities of the radiant and acoustic waves are known. The detected radiant (e.g. infrared) and acoustic signals are used to generate pulses, with the infrared initiated pulse being delayed and/or extended so as to at least partially coincide with the acoustic initiated pulse; the extension or delay time being made substantially equal to the difference in transit times of the radiant and acoustic signals in traveling between the weapon muzzle and the transducers. The simultaneous occurrence of the generated pulses is detected to provide an indication of the firing of the weapon. With this arrangement extraneously occurring radiant and acoustic signals detected by the transducers will not function to produce an output from the apparatus unless the sequence is correct and the timing thereof fortuitously matches the above-mentioned difference in signal transit times. If desired, the round detection information may be combined with target miss-distance information for further processing and/or recording.
U.S. Pat. No. 5,686,889 to Hillis described how firing of small arms results in a muzzle flash that produces a distinctive signature conducive to automated or machine-aided detection with an IR (infrared) imager. The muzzle flash is intense and abrupt in the 3 to 5 μm band. A sniper detection system operating in the 3 to 5 μm region must deal with the potential problem of false alarms from solar clutter. Hillis proposes to reduce the false alarm rate of an IR based muzzle flash or bullet tracking system (during day time) by adding a visible light (standard video) camera. The standard video camera helps detect (and then discount) potential sources of false alarm caused by solar clutter. If a flash is detected in both the IR and the visible spectrum at the same time, then the flash is most probably the result of solar clutter from a moving object. If a flash is detected only in the IR, then it is most probably a true weapon firing event.
US Patent Application Publication No. 2011/0170798 to Tidhar discloses a device and a method for use in detection of a muzzle flash event. The device can include a Photo Detector Array (PDA), sensitive in at least a portion of the NIR and SWIR spectrum, and a filter of electromagnetic radiation selectively passing in this portion a spectral range of low atmospheric transmission, the PDA has an integration time shorter than a duration of the muzzle flash event.